U.S. Pat. No. 3,794,465 discloses photographic film units which incorporate intermediate the photosensitive silver halide emulsion layer and a transparent support, a substantially colorless precursor of a dye. This precursor is converted into a dye, a colored species which will absorb light which otherwise might fog the photoexposed silver halide emulsion. Since the precursor is initially colorless, the location of the precursor in the film unit does not interfere with the exposure of the silver halide emulsion. The precursor is converted to its colored form by contact with alkali.
In a preferred embodiment, the dye produced from the above-described precursor is a silver halide desensitizing agent. Thus, instead of a light filtering mechanism, a silver halide desensitizing mechanism may be employed to protect the silver halide emulsion layer from post-exposure fogging. While the same materials can be employed to perform the two described functions, it should be understood that the quantity employed is generally much less for the silver halide desensitizing agent than for the filter dye.
The present invention is directed to novel compositions for use as the above-described dye precursors.